1. Field of the Invention
The present invention relates to an optical pickup device, and more particularly to an optical pickup device which uses a dual grating adapted to split, into three beams, each of two light beams of different wavelengths selectively emitted from a dual wavelength light source module, while including a hologram capable of allowing a typical photodetector having 8-section patterns to detect both the three beams split from one light beam and the three beams split from the other light beam.
2. Description of the Related Art
Generally, optical pickup devices are adapted to reproduce signals recorded on an optical disc and to record signals on an optical disc. For such optical pickup devices, products for a compact disc (CD) and products for a digital versatile disc (DVD) are widely used.
Although products for DVDs have a superior performance in association with DVDs' high capacity, they cannot exist on the market unless they are compatible with products for CDs because most users are more familiar with products for CDs than products for DVDs, which are inexpensive and conventionally widely distributed. To this end, most of the currently commercially available optical pickup devices are of a compatible type so that they are usable for both the DVDs and the CDs.
FIG. 1 schematically illustrates an example of a conventional compatible optical pickup device.
Referring to FIG. 1, the conventional optical pickup device includes two light source modules 10 and 20 respectively adapted to generate light beams having different wavelengths. One of the light source modules, that is, the light source module 10, is a light source module for CDs having a wavelength of 780 nm, whereas the other light source module, that is, the light source module 20, is a light source module for DVDs having a wavelength of 650 nm.
The light beam emitted from the light source module 10 for CDs is incident onto a beam splitter 14 for CDs after being split into at least three beams, for example, zero, +1st, and −1st-order diffracted beams, by a grating 12 for CDs. The light beam is reflected by the beam splitter 14 for CDs so that its travel path is bent toward a mirror 30.
After being reflected by the mirror 30, the light beam for CDs travels toward an optical disc D as its travel path is bent by the mirror 30. The light beam is then focused onto a spot on the optical disc D through an objective lens 50. The focused light beam strikes a signal track on the optical disc D, and is then reflected therefrom, so that it is re-incident onto the mirror 30 via the same path as described above. The light beam is reflected again from the mirror 30, and then is incident onto a sensor lens 50 after passing through the beam splitter 14 for CDs. The sensor lens 50 condenses the light beam incident thereto, and sends the condensed light beam to a photodetector 60 which, in turn, detects the light beam received thereto, and generates an electrical signal, based on the detected light beam.
On the other hand, the light beam emitted from the light source module 20 for DVDs is incident onto a beam splitter 24 for DVDs after being split into at least three beams, for example, zero, +1st, and −1st-order diffracted beams, by a grating 22 for DVDs. The light beam is reflected by the beam splitter 24 for DVDs so that its travel path is bent toward the mirror 30.
Thereafter, the light beam for DVDs is sent to the photodetector 60 in a condensed state along the same optical path as that of the light beam for CDs.
That is, the light beam for CDs is reflected by the mirror 30, so that it travels toward the optical disc D as its travel path is bent by the mirror 30. The light beam is then focused onto a spot on the optical disc D through the objective lens 50.
The focused light beam strikes a signal track on the optical disc D, and is then reflected therefrom, so that it is re-incident onto the mirror 30 via the same path as described above. The light beam is reflected again from the mirror 30, and then incident onto the sensor lens 50 after passing through the beam splitter 14 for CDs. The sensor lens 50 condenses the light beam incident thereto, and sends the condensed light beam to a photodetector 60 which, in turn, detects the light beam received thereto, and generates an electrical signal, based on the detected light beam.
For the photodetector 60, a photodetector having 8-section patterns is typically used because the light beam emitted from the light source module 10 for CDs and the light beam emitted from the light source module 20 for DVDs are focused onto a spot on the photodetector 60 after traveling along the same optical path.
The conventional optical pickup device having the above mentioned configuration is compatible with both the CDs and the DVDs because it operates by use of the light beam emitted from the light source module 10 for CDs upon performing a reproduction/recording operation for a CD, while operating by use of the light beam emitted from the light source module 20 for DVDs upon performing a reproduction/recording operation for a DVD.
In the above mentioned conventional optical pickup device, however, its light source modules for CDs and DVDs have separate configurations, respectively. Also, separate gratings and separate beam splitters are used for CDs and DVDs, respectively. For this reason, the conventional optical pickup device uses an increased number of optical elements, so that it has a complex configuration while having problems of a degradation in assemblability and a degradation in productivity.
Furthermore, the increased number of optical elements causes an increase in manufacturing costs, thereby resulting in a reduction in competitiveness in terms of price.
FIG. 2 schematically illustrates an example of a conventional optical pickup device having a dual wavelength light source module.
Referring to FIG. 2, the conventional optical pickup device includes a dual wavelength light source module 70 for emitting a selected one of two light beams, that is, a light beam having a wavelength of 650 nm for DVD-family optical discs and a light beam having a wavelength of 780 nm for CD-family optical discs. In this case, the light beam for CDs and the light beam for DVDs are used only for reproduction purposes.
A light beam, which is emitted from the dual wavelength light source module 70, is incident onto a beam splitter 74 after being split into three beams by a grating 72. The light beam is reflected by the beam splitter 74 so that its travel path is bent toward a mirror 30. The grating 72 is designed to optimize the light beam for CDs, so as to enable tracking of the light beam for CDs.
After being reflected by the mirror 30, the light beam travels toward an optical disc D as its travel path is bent by the mirror 30. The light beam is then focused onto a spot on the optical disc D through an objective lens 50.
The focused light beam strikes a signal track on the optical disc D, and is then reflected therefrom, so that it is re-incident onto the mirror 30 via the same path as described above. The light beam is reflected again from the mirror 30, and then incident onto a sensor lens 50 after passing through the beam splitter 74.
The sensor lens 50 condenses the light beam incident thereto, and sends the condensed light beam to a photodetector 80 which, in turn, detects the light beam received thereto, and generates an electrical signal, based on the detected light beam. The light beam for CDs and the light beam for DVDs are focused on the photodetector 80 at different spots, respectively, because their emission points are spaced apart from each other by a certain distance. For this reason, a photodetector having 10-section patterns is typically used for the photodetector 80.
In this conventional optical pickup device having the above mentioned configuration, only one grating and only one beam splitter are used because it uses one dual wavelength light source module. Accordingly, this optical pickup device has advantages of a simple configuration, an improvement in assemblability, and an improvement in productivity in accordance with a reduced number of optical elements.
However, such an optical pickup device using a conventional dual wavelength light source module has a drawback in that it is used only for reproduction purposes.
Also, the grating used in this optical pickup device is designed to optimize the light beam for CDs. That is, the conventional grating is adapted to split a light beam for CDs into 3 diffracted beams, so as to enable tracking of the light beam for CDs. Of course, the light beam for DVDs is also split while passing through the grating, in accordance with the characteristics of the grating. However, the division of the light beam for DVDs cannot be achieved in an optimized state because the grating is designed to optimize the light beam for CDs. For this reason, the conventional grating has a difficulty in splitting both the light beam for CDs and the light beam for DVDs in an optimized state.
Furthermore, although the conventional optical pickup device uses a typical photodetector having 10-section patterns, this photodetector has a drawback in that it is adapted only for reproduction purposes, so that it cannot be used for recording purposes.
Meanwhile, Korean Patent No. 267233 discloses a technique in which light beams respectively emitted from different light sources are rendered to be focused onto a photodetector at the same spot, using a hologram.
However, this patent has problems of a complex configuration caused by use of two light source modules, and, thus, a degradation in assemblability, a degradation in productivity, and high manufacturing costs.